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The vast majority of cases are in the southeastern state of Minas Gerais, where authorities had confirmed 97 cases as of Friday. Of those, 40 died.

The Health Department of Sao Paulo on Monday said it has now confirmed six cases of the disease, four of whom became infected in Minas Gerais. All of the patients died. The state of Espirito Santo has also recorded one case.

Much of Brazil is considered at risk for yellow fever, but the country has not seen this large an outbreak since 2000. The World Health Organization has said it expects the mosquito-borne to spread to more states.